In the manufacture of a microelectronic device, circuit packages are formed having an array of pins, pads, or lands that make contact with the rest of the device, typically through a printed circuit board. After production, each package must be tested to ensure that it has been manufactured correctly and all electrical contacts operate effectively.
To perform the tests, the packages may have lands, pads, or solder balls specifically included in the package for test purposes (“test contacts”). There is also an array of contacts that are used for normal operations, often in the form of solder balls.
In an integrated circuit test system, the test probes often comprise spring and sleeve connectors in which one or both ends of a cylindrical probe are spring-loaded to apply pressure against the test contacts of the package. One common type of spring-loaded test probe is referred to as a pogo pin. The test probes are mounted adjacent to a circuit board or attached to a substrate in a socket that aligns each probe in the proper position with respect to each respective contact so that when the package is pressed against the socket, each probe will effectively contact its respective contact such as a land, ball or pad. The probes also have a shaped tip so that when the probes are pressed against the package, the spring pressure will cause the tip to break through any oxide that has formed on the surface of the associated contact to ensure a good electrical connection. Signals are sent or received through the probes to test the device.
The tip of a test probe wears with each contact against the associated contact such as a solder ball test contact; the tip may also collect contaminants from the package connection. As a result, each test probe has a limited number of contacts and therefore a limited number of package tests that it can perform, after which the test probe is ineffective and must be replaced. With thousands of test probes in each socket, test probe replacement is a factor in the cost of device manufacturing. The pogo pin is used for many different testing functions, including burn in, class test, and system test. Because there are thousands of pins per socket, the pins represent a significant part of the cost of unit interface tooling (UIT).
As the test probe is repeatedly used, there are several different mechanisms that wear and contaminate the tip of the probe, rendering it unreliable. Typical plunger or cylinder materials include Pd alloy, steel, or Cu/Be alloy. In some cases, Au/Ni layers are coated over the tip to provide oxidation protection and improve electrical conduction. With repeated cycling, the plunger can degrade and become dulled, leading to an ineffective contact between the test probe tip and the tested unit. There may be an increase in the contact resistance (Cres) at the tip of the test probe. An initially sharp shape becomes dulled and no longer penetrates the solder ball. In addition, any coating layers on the probe tip may be worn off.
Each time the probe tip contacts a new package contact, it may also pick up contaminants. Sn, PbO and SnO are among the most common contaminants that a probe tip can pick up from a solder ball. Also, with the increasing use of No-Clean Paste (NCP) for Ball Grid Array (BGA) packages, a substantial amount of organic residue such as rosin remains on the solder ball and can be transferred to the probe tip. This can cause a socket open failure. The contaminants can be controlled by cleaning; however, regular cleaning is very expensive and time consuming, it takes the tool out of service and further wears on the tip. Mechanical rubbing, for example, can accelerate pogo-pin wearing, and speed up pin degradation failures.
It would be desirable to provide a convenient and cost effective kit and method for cleaning and coating a tip of a test probe in an integrated circuit package test system that removes contaminants and provides protection to the test probe, allowing for extended use.